Current fireworks get their red hue primarily from strontium monochloride, which can generate cancer-causing fallout.

Credit: Shutterstock

SEEING RED

Current fireworks get their red hue primarily from strontium monochloride, which can generate cancer-causing fallout.

Credit: Shutterstock

Makers of fireworks and flares have long believed that the beautiful red color in their explosions could be attained only with chlorine-based compounds. But after these ingredients combust, they can transform into cancer-causing chemicals that then fall to the Earth.

Now, new chlorine-free pyrotechnics could pave the way for a generation of red flares and fireworks that are better for the environment and for people’s health, says Jesse J. Sabatini at the U.S. Army Research Laboratory, in Maryland. Sabatini developed the red pyrotechnics with Ernst-Christian Koch at consulting firm Lutradyn, in Kaiserslautern, Germany (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201505829).

Currently, red fireworks get their hue primarily from strontium monochloride, which is produced by burning strontium compounds with polyvinyl chloride and a variety of other pyrotechnic ingredients. Unfortunately, the combustion of these mixtures produces a variety of polychlorinated aromatic chemicals, including some potent carcinogens.

To make the more environmentally friendly fireworks, the researchers focused on strontium monohydroxide, a compound that scientists had long believed was only a minor contributor to the red color of pyrotechnics. According to Koch, for years, scientists hadn’t realized that strontium monohydroxide also strongly flared red because its sister product, strontium oxide, produces an orange-red color that fireworks-makers try to avoid.

Sabatini, Koch, and coworkers formulated the new explosive by replacing polyvinyl chloride on the old ingredient list with either hexamine, a preservative in citrus washing solutions, or 5-amino-1H-tetrazole, an airbag propellant. The replacement successfully removes chlorine and helps produce strontium monohydroxide when the overall concoction is ignited, producing bright red fireworks. As an added bonus, the new formulation also avoids the production of unwanted orangey strontium oxide, Koch says.

“It’s very challenging to go from something that works on the bench to something that works on a large-scale,” comments David E. Chavez, a chemist at Los Alamos National Laboratory who was not involved in the research. But this new combustible formulation might translate to large-scale fireworks displays readily, he says. Because hexamine and 5-amino-1H-tetrazole are widely used in the chemical industry, the new formulation could easily be adopted by pyrotechnic producers.

The potential benefit is not just to those putting on Fourth of July and New Year’s Eve fireworks displays, Chavez adds. The military is also a large consumer of red flares, particularly for training purposes. “Training areas get fallout [from flares] over and over again,” he says. So much so, “that it can be an issue for environmental clean-up,” Chavez adds.

Next up, researchers may want to focus on blue and green fireworks, many of which also employ chlorine in their formulations. One can hope that this work will encourage others to formulate more environmentally friendly fireworks of other colors with similar strategies, says Nigel Davies, a retired pyrotechnics instructor at the Defence Academy of the United Kingdom.

I applaud the improvement and yearn for an incentive to formulate other less toxic pyrotechnics. It is a tricky public relations statement to boast "fewer carcinogens cascading down on your celebration!"

It's interesting to finally see something along these lines after advocating in my own quiet way for such things to be done. This (environmental consideration) was never rocket science. The direction could easily be seen 25-30 years ago to me, and others.

A waggle of my finger to the writer Sara Everts for her contention in the first paragraph--- "Makers of fireworks and flares have long believed that the beautiful red color in their explosions could be attained ONLY with chlorine-based compounds."
As a minor student of pyrotechnic literature and formulas I can tell you that her statement is incorrect.

There are quite a few formulas for red which do not rely on chlorine donors. Certainly, one may achieve color enhancement with chlorine donors, but they are not necessary, ESPECIALLY with the color red. The introduction of metal fuels and extra chlorine donors has brightened and deepened color in the last 20 or so years of fireworks, but they're not necessary. They're not the "only" way to do red.

Stars, or the pellets made of pyrotechnic mixtures with a binder, are not supposed to explode but to burn brightly, as are flares. If they act as explosives, the maker has performed their job incorrectly. Pyrotechnic stars and flares may be classified as explosives for purposes of transportation regulations, but they are not designed to explode and don't have a big history of doing so. Burst charges that burst the aerial shell, ignite the stars and fling them outward are more what you would think of as "explosive". There are a number of specific descriptive terms for different levels of energetic decomposition that are confusing to most laypeople and even regulators and authorities having jurisdiction.

Sarah also wrote: "But after these ingredients combust, they can transform into cancer-causing chemicals that then fall to the Earth."

With all due respect, ma'am, can you present any literature that shows these to be a health risk to the public, wildlife or broader ecosystem in the amounts that are used? As I am a reasonable person I would like like to hear some reasonable information that we should be concerned about fireworks instead of much larger contributors to these pollutants and carcinogens of concern.

If readers and Sarah Everts would like to begin to learn about what really goes on in the pyrotechnic world, I would humbly suggest that they consider joining the Pyrotechnics Guild International, a fine organization with many members dedicated to passing on knowledge of the art and science of pyrotechnics.

Their annual convention is a week devoted to fireworks, put on by volunteers and paid staff who coordinate everything from classes, workshops and competitions, to product demonstrations and huge displays. ..... And if you have some training and follow safety rules, you can shoot fireworks to your heart's content.